Reaffirming his national political ambitions, Sen. Marco Rubio accused Democrats on Friday of threatening the American dream as he campaigned across New Hampshire, appearing in the first-in-the-nation presidential primary state for the first time in 18 months.

The Florida Republican also jabbed at former Secretary of State Hillary Rodham Clinton, considered the overwhelming favorite to win the next Democratic presidential nomination if she chooses to run, in a speech to hundreds of Republicans gathered in New Castle, along New Hampshire's seacoast.

"They're threatening to nominate someone now who wants to take us to the past — to an era that's gone and never coming back," Rubio, 43, told the Rockingham County Republican Committee, referring to Clinton. "The road we're on right now is a road that will rob us of the American dream."

The appearance marks the clearest sign yet of Rubio's interest in a 2016 presidential bid as he beefs up political organization and charts an aggressive role in this fall's midterm elections.

Rubio attended three fundraisers on Friday to benefit New Hampshire Republicans, earning a private audience with key activists, donors and elected officials who play outsized roles in the selection of the GOP's next presidential nominee. The state's 2016 presidential primary is roughly a year and a half away, but prospective candidates have begun to flock to the state in recent months to secure an early advantage with key players.

Rubio is the first in the group of mainstream Republicans to appear in New Hampshire this year. Mike Huckabee, a former Arkansas governor and ordained Baptist minister, and tea party favorites Kentucky Sen. Rand Paul and Texas Sen. Ted Cruz have visited several times.

Some New Hampshire Republicans report some skepticism about Rubio, whom they describe as a relatively inexperienced leader who has failed to impress in key moments.

"He's sort of a victim of his own success. He was considered this hotshot rising star. Then a couple of issues like immigration haven't gone very far, so some people think his stock is falling," Steve Duprey, the state's Republican National committeeman said of Rubio. "To me, he comes across as a serious and thoughtful, mainstream conservative."

At the same time, Rubio has reshuffled his staff and directed his political resources to three key Senate races this year, including a GOP primary in Iowa, the state that hosts the first caucuses of the presidential primary season. Taken together, his actions are part of an effort to strengthen his standing in a potentially crowded 2016 presidential field after a year in which he saw his popularity slip over his backing of an immigration overhaul.

The renewed push also comes as the GOP establishment turns its attention to the freshman senator's onetime mentor, former Florida Gov. Jeb Bush. Many party insiders and major donors are signaling their preference for Bush, the brother of President George W. Bush, which could threaten a potential Rubio candidacy.

For now, Rubio's advisers say his political focus remains on helping Republicans retake the Senate in November. His political action committee is backing candidates in Arkansas, Colorado and Iowa — efforts that aides acknowledge could buoy a presidential campaign should Rubio run.

In Washington, Rubio has muscled his way to the forefront of major domestic and foreign policy debates, becoming a leading Republican voice for more robust action in geopolitical hot spots from Venezuela to Russia to China. Next week, he will detail his ideas to bolster retirement security and overhaul entitlement programs.

"The true American dream is not about what government can do for us," he said, "but what we can do for ourselves and for our nation together."